This invention relates to a controllable stabilizer, and relates more particularly but not exclusively to a controllable direction deviator for use in steering the direction in which a well is drilled, e.g. to produce a deviated oil well.
Modern drilling techniques for the creation of wells between a surface drilling station and oil-bearing geological strata horizontally remote from the surface drilling station require close control of the drilled well to a pre-planned trajectory. Known directional drilling techniques typically involve the use of a downhole drilling motor and a bent sub, with the drill pipe being non-rotating and the rotational position of the bent sub being used to determine the direction of deviation (i.e the direction and angular extent to which the currently projected drilling direction deviates from a straight-ahead projection of the most recently drilled section of the well; directional drilling may thus be considered as downhole steering of the drill).
Prior to the use of downhole motors with bent subs for directional drilling, whipstocks were used to deviate rotating drilling assemblies. The disadvantages of whipstocks were that they required orientation by drillstring movements initiated from the surface station, and that the whipstocks had to be reset (re-orientated) after the drilling of relatively short distances.
It is an object of the invention to provide a substitute for known directional drilling techniques, in the form of a controllable stabilizer for producing a radial load in a rotatable drillstring or drill shaft such as to control the deviation of a well being drilled. It is a further object of the invention to provide a directionally-controlled eccentric which is also applicable to producing directionally controlled eccentricity In circumstances which may not involve drilling.